A tire puncture—that is to say a hole in a tire, the effect of which is that inflation gas escapes and the tire loses inflation pressure—is one of the most troublesome kinds of damage experienced by tire users. If the loss of pressure is great, it may force the tire user to replace the tire on the spot, in order to avoid damaging the tire or even the vehicle fitted with the tire. Depending on the circumstances, this need to replace the tire without delay may prove dangerous (for example when the puncture occurs on a very busy road with no hard shoulder) or penalizing (for example, during a motor race).
Confronted with this very long-standing problem, tire manufacturers have developed a broad spectrum of solutions. Among the oldest solutions are, in particular, tires with double chambers, which have two non-communicating chambers each of which can be inflated. When one of the chambers is punctured but not the other, the tire does not fully deflate, thus allowing continued running “in degraded mode”, i.e. the tire can still run, but its running performance is inferior to the performance obtained when the tire is inflated to its service pressure. By way of example of this type of solution, mention may be made of U.S. Pat. No. 2,874,744, U.S. Pat. No. 3,018,813, U.S. Pat. No. 3,025,902 and U.S. Pat. No. 3,901,750. However, these solutions have the disadvantage of being very complicated to manufacture and have not found widespread use.
More recently, it has been proposed that use be made of structures capable of running without any inflation pressure, such as, for example, self-supporting tires like the one described in U.S. Pat. No. 6,688,354. Unfortunately, the reinforcing of the sidewalls of these tires generally has the consequence that other performance aspects of the tire are penalized, e.g. the rolling resistance of the tire or the ride comfort may be degraded even when running at normal pressure. In other words, the performance of the tire during “normal running” (that is to say when the tire is running inflated at its service pressure) is penalized in order to allow an improvement in performance when running “in degraded mode” even though this second running mode is the exception and may never even be experienced throughout the life of the tire.
This difficulty is overcome by another solution in which the tire is provided with internal supports which support the tread when the tire inflation pressure drops. The Pax System™ developed by Michelin (see, for example, U.S. Pat. No. 5,787,950) is a well known example of this technology. Its disadvantage lies in that it requires special tooling to fit the tire and in that it increases the weight of the tire-wheel assembly.
Yet another approach, which has found application particularly in the field of motor sport, has been to use a foam support which is compressed when the tire is inflated but which expands as the inflation pressure decreases, to the point where it fills the interior of the tire and bears some of the load thereof (see, for example, U.S. Pat. No. 3,426,821). This technology has the advantage of allowing use under extreme conditions, but it has the disadvantage of being relatively complicated to fit.
Finally, it is known to apply sealing fluids to the interior surfaces of the tire. In the event of a puncture, the fluid flows towards the hole in the wall of the tire and seals it U.S. Pat. No. 4,206,796 provides an example of this. One of the disadvantages with this technology lies in the fact that it is suited first and foremost to punctures near the crown of the tire and is less well suited to sidewall punctures, because the sealing fluid has a tendency, under the effect of centrifugal force, to move towards the crown and to fail to cover the interior of the sidewall. In addition, this solution is reserved rather for small punctures in the tire (typically, for holes not exceeding 5 mm in diameter).